Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability, resulting from a mutation in the FMR1 gene on the X chromosome. Males are more severely affected on average than females. Language impairments are common and often more severe than cognitive-level expectations. These language impairments interfere with the acquisition of literacy skills, learning, social interaction, and adaptive functioning. The proposed project extends the previously funded, Language Development in Fragile X Syndrome. We will continue the longitudinal investigation of males with FXS into adulthood and begin tracking the trajectories of females with FXS, who have been under-studied, especially in the adult years. We will focus on language development within the broader framework of an examination of the transition from high school into adulthood and the experiences of individuals with FXS in contexts requiring and promoting independence. We also propose to expand our assessment of language to include measures of pragmatics and literacy, which are areas of challenge, even for females with FXS who do not have an intellectual disability. The project has four specific aims. (1) Describe the development of language, literacy, and the capacity for independent functioning in FXS during the transition into adulthood. We will use a variety of measurement strategies and provide the most comprehensive characterization to date of the transition to adulthood for FXS. (2) Evaluate for the first time the bidirectional relationships between the capacity for independent functioning and language and literacy. (3) Identify the determinants of within-syndrome variation in language and literacy. In doing so, we will emphasize the contributions of core domains of the FXS behavioral phenotype (i.e., auditory memory, executive function, autism symptom severity, anxiety, social avoidance, and physiological arousal), as well as the contributions of variations in the FMR1 mutation and the family context. (4) Identify sex differences in language, literacy, and the capacity for independent functioning, which are areas that have yet to be explored for the adult transition years. The target sample is 60 males and 60 females. Participants will enroll in the project in their last year of high school, which occurs between ages 17 and 22 for this population. A comprehensive, direct, multimethod, assessment of language, literacy, core features of the phenotype, the capacity for independent functioning, and the family context (with an emphasis on parental contributions) will be conducted near high school exit (T1) and then again three years later (T4). Molecular measures of the FMR1 locus will be collected at T1. Caregiver report about the level of independence displayed by the individual with FXS in meeting the demands of adult life will be collected at T1 and then annually (T2 through T4). Participating sites are University of California, Davis; University of South Carolina; and Vanderbilt University.